A conventional stacker crane is disclosed in Japanese Patent Preliminarily Publication No. 2003-237909, where a lower frame comprises a connecting frame for connecting front and rear wheel support frames, by which running wheels are supported, and where the front and rear support rods standing from the lower frame are mounted and supported by the connecting frame at their lower ends.
Another conventional stacker crane is disclosed in Japanese Patent Preliminarily Publication No. 2006-76715, where a lower frame comprises a connecting frame for connecting front and rear wheel support frames, by which running wheels are supported, and where the front and rear support rods standing from the lower frame are mounted on the top surfaces of the front and rear wheel support frames at their lower ends, and extended guide rails for guiding a platform are provided and being connected to the guide portion of the platform at the front and rear support rods.
The conventional stacker crane disclosed in the Japanese Patent Preliminarily Publication No. 2003-237909 is disposed to have the front and rear support rods mounted to and supported by the connecting frame at their lower ends. Therefore, the weight of the front and rear support rods, the upper frame, and the platform and the weight of articles held by the platform act against the connecting frame, which connects the front and rear wheel support frames for supporting the running wheels.
Since such a heavy weight acts on the connecting frame, the connecting frame must have sufficient strength for the weight, which made the connecting frame expensive and difficult to lower cost for the lower frame itself.
The conventional stacker crane disclosed in the Patent Preliminarily Publication No. 2006-76715 is disposed to have the front and rear support rods mounted on the top surface of the front and rear wheel support frames at their lower ends. Therefore, the front and rear wheel support frames have to bear the weight of the front and rear support rods, the upper frame, the platform and the weight of articles held by the platform.
Since such a heavy weight does not act on the connecting frame for connecting the front and rear wheel support frames, the connecting frame does not need to be so strong and therefore could be manufactured cheaper.
However, as mentioned above, the stacker crane disclosed in the Patent Preliminarily Publication No. 2006-76715 includes extended guide rails for guiding a platform, which are connected to the guide portion of the platform at the front and rear support rods, on the side surfaces of the front and rear wheel support frames. This stacker crane is constructed such that the platform is guided by the extended guide rails, which complicates the guiding system of the platform. Therefore, the lower frame of this conventional type of stacker crane cannot be made cheaper.